The possibility of performing measurements of properties such as pressure, temperature, volume and flow within internal body organs has become increasingly important in for example diagnosis of heart diseases.
Sensor and guide wire assemblies are guide wires that have measurement sensors located at or near their distal tips. These devices are typically used in applications to measure internal properties of internal tissues and fluids such as blood pressure. Sensor and guide wire assemblies may be introduced directly into arteries, veins or other body organs either by themselves or through catheters that have been previously positioned within a patient. A sensor and guide wire assembly is disclosed in U.S. Pat. No. 6,142,958 and a pressure sensor and guide wire assembly for biological pressure measurements is disclosed in U.S. Pat. No. 6,167,763 which hereby are incorporated by reference. These sensor and guide wire assemblies typically have an outer diameter of 0.035 mm (0.014″).
To increase the diagnostic value for many type of heart diseases and blood vessel alterations such as arteriosclerosis, it would be desirable to combine the pressure measurement with volumetric measurements. In the case of diagnosis of heart diseases so called “Pressure/Volume loops”, PV-loops, are of particular interest. An established method of estimating the volume of internal cavities of body organs, for example the heart chamber, is by measuring the conductance.
Vessel compliance is also a measure of the status of a blood vessel, in that a soft vessel will be subject to some expansion upon an increased internal pressure, whereas a stiff vessel, indicating arteriosclerosis, would be subject to less expansion. It would be desirable to be able to measure such vessel compliance in a reliable way.
U.S. Pat. No. 6,112,115 disclose a method of producing PV-loops using a conductance catheter and a micro pressure catheter inserted in said conductance catheter. The usage of several different catheters adds complexity, and possibly discomfort for the patient.
In U.S. Pat. No. 5,902,248 (Millar) the inventors describe a catheter tip pressure transducer also including electrodes enabling conductance measurements. However, a catheter lacks the flexibility of sensor and guide wire assemblies and thus less suitable for some applications requiring a very flexible distal region. Furthermore, this patent is directed to use in animals, in particular mice.
In order to create a minimal invasive method of diagnosis it is highly desirable to also include the ability for conductance measurements in the sensor and guide wire assembly.